Coherent transport of an excitation through a network corresponds to continuous-time quantum walk on a graph, and the transport properties of the system may be radically different depending on the graph and on the initial state. The transport efficiency, i.e., the integrated probability of trapping at a certain vertex, is a measure of the success rate of the transfer process. Purely coherent quantum transport is known to be less efficient than the observed excitation transport, e.g., in biological systems, and there is evidence that environmental noise is indeed crucial for excitation transport. At variance with this picture, we here address purely coherent transport on highly symmetric graphs, and show analytically that it is possible to enhance the transport efficiency without environmental noise, i.e., using only a minimal perturbation of the graph. In particular, we show that adding an extra weight to one or two edges, depending on whether the initial state is localized or in a superposition of two vertex states, breaks the inherent symmetries of the graph and may be sufficient to achieve unit transport efficiency. We also briefly discuss the conditions to obtain a null transport efficiency, i.e., to avoid trapping.Coherent transport of an excitation through a network corresponds to continuous-time quantum walk on a graph, and the transport properties of the system may be radically different depending on the graph and on the initial state. The transport efficiency, i.e., the integrated probability of trapping at a certain vertex, is a measure of the success rate of the transfer process. Purely coherent quantum transport is known to be less efficient than the observed excitation transport, e.g., in biological systems, and there is evidence that environmental noise is indeed crucial for excitation transport. At variance with this picture, we here address purely coherent transport on highly symmetric graphs, and show analytically that it is possible to enhance the transport efficiency without environmental noise, i.e., using only a minimal perturbation of the graph. In particular, we show that adding an extra weight to one or two edges, depending on whether the initial state is localized or in a superposition of two vertex states, breaks the inherent symmetries of the graph and may be sufficient to achieve unit transport efficiency. We also briefly discuss the conditions to obtain a null transport efficiency, i.e., to avoid trapping.

arXiv:2205.09408Physical review. EAug 22, 202210 citations

Dephasing-assisted selective incoherent quantum transport

Naghi Behzadi, Bahram Ahansaz, H. Kasani

Selective energy transport throughout a quantum network connected to more than one reaction center can play an important role in many natural and technological considerations in photosystems. In this work, we propose a method in which an excitation can be transported from the original site of the network to one of the reaction centers arbitrarily using independent sources of dephasing noises. We demonstrate that in the absence of dephasing noises, the coherent evolution of the system does not have any role in energy transport in the network. Therefore, incoherent evolution via application of dephasing noises throughout a selected path of the network leads to complete transferring of the excitation to a desired reaction center.Selective energy transport throughout a quantum network connected to more than one reaction center can play an important role in many natural and technological considerations in photosystems. In this work, we propose a method in which an excitation can be transported from the original site of the network to one of the reaction centers arbitrarily using independent sources of dephasing noises. We demonstrate that in the absence of dephasing noises, the coherent evolution of the system does not have any role in energy transport in the network. Therefore, incoherent evolution via application of dephasing noises throughout a selected path of the network leads to complete transferring of the excitation to a desired reaction center.

arXiv:1412.3745Physical Review EOct 5, 20153 citations

Energy transport in quantum many-body systems

Klée Pollock

Jan 1, 20260 citations

Coherent ground-state transport of neutral atoms

X. X. Li, Jia-Bin You, Xiao‐Qiang Shao +1 more

Quantum state transport is an important way to study the energy or information flow. By combining the unconventional Rydberg pumping mechanism and the diagonal form of van der Waals interactions, we construct a theoretical model via second-order perturbation theory to realize a long-range coherent transport inside the ground-state manifold of neutral atoms systems. With the adjustment of the Rabi frequencies and the interatomic distance, this model can be used to simulate various single-body physics phenomena such as a Heisenberg $XX$ spin chain restricted in the single-excitation manifold, coherently perfect quantum state transfer, the parameter-adjustable Su-Schrieffer-Heeger model, and chiral motion of atomic excitation in a triangle by varying the geometrical arrangement of the three atoms, which effectively avoids the influence of atomic spontaneous emission at the same time. Moreover, the influence of atomic position fluctuation on the fidelity of quantum state transmission is discussed in detail, and the corresponding numerical results show that our work provides a robust and easily implemented scheme for quantum state transport with neutral atoms.Quantum state transport is an important way to study the energy or information flow. By combining the unconventional Rydberg pumping mechanism and the diagonal form of van der Waals interactions, we construct a theoretical model via second-order perturbation theory to realize a long-range coherent transport inside the ground-state manifold of neutral atoms systems. With the adjustment of the Rabi frequencies and the interatomic distance, this model can be used to simulate various single-body physics phenomena such as a Heisenberg $XX$ spin chain restricted in the single-excitation manifold, coherently perfect quantum state transfer, the parameter-adjustable Su-Schrieffer-Heeger model, and chiral motion of atomic excitation in a triangle by varying the geometrical arrangement of the three atoms, which effectively avoids the influence of atomic spontaneous emission at the same time. Moreover, the influence of atomic position fluctuation on the fidelity of quantum state transmission is discussed in detail, and the corresponding numerical results show that our work provides a robust and easily implemented scheme for quantum state transport with neutral atoms.

arXiv:2107.02376Physical Review AMar 8, 202227 citations

Classification and Exact Local Masking in Finite-Field Clifford Dual-Unitary Circuits

Basanta R Pahari

We classify two-qudit Clifford dual-unitary gates over the finite field $\mathbb{F}_q$ , where the local dimension $q$ is a prime power, and apply the classification to exact local masking and operator transport in homogeneous brickwork circuits. Under ordered one-qudit Clifford equivalence, the dual-unitary locus contains $q-2$ perfect-tensor cores, one rank-one core, and one SWAP core. Homogeneous repetition separates these cores into five distinct transport phases. The one-site Weyl edge channels determine exact local-masking distances. Writing $d_r(t)$ for the masking distance against output observers controlling at most $r$ sites, perfect-tensor circuits attain $d_1(t)=4t, \qquad d_2(t)=4t-2,$ whereas delayed erasers satisfy $d_1(t)=4t-2, \qquad d_2(t)=4t-4$ for $t\geq 2$ . Consequently, sufficiently short quantum messages are completely hidden from every one- or two-qudit output subsystem, even when the input is entangled with a reference, while remaining exactly recoverable from the full output. For $q=3$ , we construct an explicit perfect-tensor Clifford gate from two inverse SUM gates. Exhaustive Weyl-support searches for $t=1,2,3$ reproduce the predicted masking distances. For a coherent perturbation of this gate, local leakage scales linearly with the perturbation strength, whereas the infidelity of recovery using the ideal inverse scales quadratically near the perfect point.We classify two-qudit Clifford dual-unitary gates over the finite field $\mathbb{F}_q$, where the local dimension $q$ is a prime power, and apply the classification to exact local masking and operator transport in homogeneous brickwork circuits. Under ordered one-qudit Clifford equivalence, the dual-unitary locus contains $q-2$ perfect-tensor cores, one rank-one core, and one SWAP core. Homogeneous repetition separates these cores into five distinct transport phases. The one-site Weyl edge channels determine exact local-masking distances. Writing $d_r(t)$ for the masking distance against output observers controlling at most $r$ sites, perfect-tensor circuits attain \[ d_1(t)=4t, \qquad d_2(t)=4t-2, \] whereas delayed erasers satisfy \[ d_1(t)=4t-2, \qquad d_2(t)=4t-4 \] for $t\geq 2$. Consequently, sufficiently short quantum messages are completely hidden from every one- or two-qudit output subsystem, even when the input is entangled with a reference, while remaining exactly recoverable from the full output. For $q=3$, we construct an explicit perfect-tensor Clifford gate from two inverse SUM gates. Exhaustive Weyl-support searches for $t=1,2,3$ reproduce the predicted masking distances. For a coherent perturbation of this gate, local leakage scales linearly with the perturbation strength, whereas the infidelity of recovery using the ideal inverse scales quadratically near the perfect point.

quant-pharXiv:2607.00210Jul 2, 20260 citations

XX

spin chain restricted in the single-excitation manifold, coherently perfect quantum state transfer, the parameter-adjustable Su-Schrieffer-Heeger model, and chiral motion of atomic excitation in a triangle by varying the geometrical arrangement of the three atoms, which effectively avoids the influence of atomic spontaneous emission at the same time. Moreover, the influence of atomic position fluctuation on the fidelity of quantum state transmission is discussed in detail, and the corresponding numerical results show that our work provides a robust and easily implemented scheme for quantum state transport with neutral atoms.

We classify two-qudit Clifford dual-unitary gates over the finite field

\mathbb{F}_q

, where the local dimension

q

is a prime power, and apply the classification to exact local masking and operator transport in homogeneous brickwork circuits. Under ordered one-qudit Clifford equivalence, the dual-unitary locus contains

q-2

perfect-tensor cores, one rank-one core, and one SWAP core. Homogeneous repetition separates these cores into five distinct transport phases. The one-site Weyl edge channels determine exact local-masking distances. Writing

d_r(t)

for the masking distance against output observers controlling at most

r

sites, perfect-tensor circuits attain

d_1(t)=4t, \qquad d_2(t)=4t-2,

whereas delayed erasers satisfy

d_1(t)=4t-2, \qquad d_2(t)=4t-4

for

t\geq 2

. Consequently, sufficiently short quantum messages are completely hidden from every one- or two-qudit output subsystem, even when the input is entangled with a reference, while remaining exactly recoverable from the full output. For

q=3

, we construct an explicit perfect-tensor Clifford gate from two inverse SUM gates. Exhaustive Weyl-support searches for

t=1,2,3

reproduce the predicted masking distances. For a coherent perturbation of this gate, local leakage scales linearly with the perturbation strength, whereas the infidelity of recovery using the ideal inverse scales quadratically near the perfect point.